Mackinawite

Mackinawite is an iron nickel sulfide mineral with formula (Fe,Ni)1 + xS (where x = 0 to 0.11). It crystallizes in the tetragonal crystal system and occurs as opaque bronze to grey-white tabular crystals and anhedral masses. It has a Mohs hardness of 2.5 and a specific gravity of 4.17.

Occurrence

It occurs in serpentinized peridotites as a hydrothermal alteration product. It also is found in the reducing environment of fine grained river sediments, possibly produced by the action of magnetotactic and sulfate-reducing bacteria. It has also been reported from meteorite occurrences. It occurs in association with chalcopyrite, cubanite, pentlandite, pyrrhotite, greigite, maucherite and troilite.[1]

It was first described in 1962 for an occurrence in the Mackinaw mine, Snohomish County, Washington for which it was named.[3]